ABSTRACT
Purpose: The optimal surgical technique for unstable acromioclavicular (AC) and coracoclavicular (CC) joint injuries has not yet been established. The biomechanical and radiographic effect of the LockDown device, a synthetic ligament for AC joint reconstruction, was evaluated to assess the optimal surgical technique for unstable AC and CC joint injuries. It was hypothesized that the LockDown device would restore AC joint kinematics and radiographic stability to near native values. Methods: Three fresh frozen cadaveric torsos (6 shoulders) modelled CC joint motion in their "native," "severed," and "reconstructed" states. The effects of stressed and unstressed native, severed, and reconstructed conditions on AC separation and CC distances in anteroposterior, mediolateral, and inferosuperior directions during shoulder abduction, flexion, and scaption were assessed. The analysis of variance (p, 0.05) was used to compare CC distance and peak AC distance in anteroposterior, mediolateral, and inferosuperior directions during shoulder flexion, abduction, and scaption measurements among native, severed, and reconstructed states with unstressed and stressed Zanca radiographic views. Results: From radiographic analyses, the CC distance was significantly greater (p=0.001) across the surgical state in stressed versus unstressed views. Mean difference between stressed and unstressed views was 1.8 mm in native state, 4.1 mm in severed state, and 0.9 mm in reconstructed state. The CC distance was significantly greater in the "severed" state (10.4 mm unstressed; 14.5 mm stressed) compared to the "native" state (p=0.016) (6.5 mm unstressed; 8.3 mm stressed) and compared to the "reconstructed" state (p=0.005) (3.1 mm unstressed; 4.0 mm stressed) and significantly less (p=0.008) in the "reconstructed" state compared to the "native" state. CC distances decreased from native to reconstructed, an average of 3.3 mm for unstressed and 4.3 mm for stressed. On average, peak AC joint separation distance in anteroposterior, mediolateral, and inferosuperior directions during shoulder-abduction, flexion, and scaption was shown to be restored to 11.5 mm of native values after reconstruction with LockDown device. Conclusion: Reconstruction of AC joint with LockDown synthetic ligament restores motion of clavicle and acromion to near native values, thereby decreasing scapular dyskinesis and enhancing AC joint stability.
ABSTRACT
BACKGROUND: Graft-tunnel mismatch (GTM) is a condition in which the anterior cruciate ligament (ACL) graft is either too long or too short. GTM is particularly problematic when bone-patellar tendon-bone grafts are used because of a potential compromise in fixation of the bone plug on the tibia. HYPOTHESIS: The Blumensaat line (BL), a radiographic landmark representing the roof of the intercondylar fossa, will accurately approximate the native ACL (nACL) length and may aid in the prevention of GTM. STUDY DESIGN: Cohort study (diagnosis); Level of evidence, 3. METHODS: A total of 130 patients (66 males, 64 females) underwent direct measurement of the nACL during knee arthroscopy. The lengths of the nACL and patellar ligament (PL) were measured intraoperatively, and BL length was measured on lateral knee radiographs. The nACL length was compared with PL and BL lengths to calculate the absolute difference (AD). Mean AD was calculated and used to determine mean percentage difference (MPD). Pearson correlation coefficients (CC) between BL, PL, and nACL length were calculated, along with inter- and intraobserver reliability coefficients for the measurement of BL. RESULTS: For male patients, the mean length of the nACL was 32.5 mm, BL was 30.4 mm, and PL was 49.2 mm. The AD between the BL and nACL was 2.4 ± 1.3 mm, MPD was 2.6% ± 1.9%, and CC was 0.88. The CC between the PL and nACL was 0.08. For female patients, the mean length of the nACL was 30.2 mm, BL was 27.5 mm, and PL was 44.4 mm. The AD between the BL and nACL was 2.7 ± 1.7 mm, MPD was 4.5% ± 2.4%, and CC was 0.93. The CC between the PL and nACL was 0.1. The inter- and intraobserver reliability coefficients for the measurement of BL were 0.86 and 0.83, respectively. CONCLUSION: A strong correlation was found between BL and nACL with a high inter- and intraobserver reliability. This correlation provides a simple and reliable method to closely approximate nACL length before reconstruction and may aid in the prevention of graft-tunnel mismatch.
ABSTRACT
Elucidation of the mechanisms governing expression of the human telomerase reverse transcriptase (hTERT) is important for understanding cancer pathogenesis. Approximately 90% of tumors express hTERT, the major catalytic component of telomerase. Activation of telomerase is an early event, and high levels of this activity correlate with poor prognosis. Recent studies have shown that the transcription factors c-Myc and Mad1 activate and repress hTERT, respectively. It is not clear how these transcription factors compete for the same recognition sequence in the hTERT core promoter region. Studies have shown that the combined expression of SV40 large T antigen (T-Ag), hTERT, and H-Ras is able to transform human cells. In this study, we used a distinct human cell type, WI-38 fetal lung fibroblasts used extensively for senescence studies. We transduced cells with amphotropic retroviral constructs containing SV40 T antigen, hTERT, and activated H-ras. Transduced cells exhibited anchorage independence in soft agar and expressed increased levels of c-Myc and endogenous hTERT. These effects were observed by 25 population doublings (PDs) following the establishment of the neoplastic cell line. During the process of transformation, we observed a switch from Mad1/Max to c-Myc/Max binding to oligonucleotide sequences containing the hTERT promoter distal and proximal E-boxes. c-Myc can bind specifically to the hTERT promoter in vitro, indicating that c-Myc expression in tumors may account for the increased expression of hTERT observed in vivo. These findings indicate that the widely used model system of WI-38 fibroblasts can be employed for transformation studies using defined genetic elements and that the endogenous hTERT and c-Myc are induced in these cells during early tumorigenesis. Such studies should have important implications in the mechanisms of hTERT and c-Myc induction in the beginning stages of tumorigenesis and facilitate extension of these studies to novel models of tumorigenesis in cellular senescence.
